Television deflection power recovery circuit



TELEVISION DEFLECTION POWER RECQYERY CIRCUIT Filed April 30, 1949 INVENTOR Amw /7. 5,4200

TTORNEY Patented June 5, 1951 assent TELEVISION DEFLECTION POWER RECOVERY CIRCUIT Allen A. Barco, Princeton, N. J assignor to Radio Corporation of America, a corporation of Delaware Application April 30, 1949, Serial No. 90,572

The present invention relates to electrical damping systems of the reaction scanning power recovery type and more particularly to electromagnetic cathode ray beam deflection circuits of the type employed in television systems wherein a portion of the damped reactive energy in the deflection system is fed back for utilization by the deflection circuit to thereby improve the overall operating efliciency of the system.

Generally speaking, in electrical circuits wherein some form of damping action is required, the overall efficiency of operation is considerably lowered because of the energy dissipated in the damping circuits, this energy not being gainfully utilized. In early television practice, cathode ray electromagnetic beam deflection systems suffered substantial losses in this respect, which in turn stimulated the development of power recovery deflection systems in which some of the stored electromagnetic reactive energy, normally dissipated in the damping system, is capacitively stored and employed to effect a boost in the B supply voltage applied to the vacuum tube driving the deflection system. Such power recovery or power feedback systems have greatly improved the operating efficiencies obtainable in deflection systems as a whole. However, most prior art systems of this kind require the utilization of a deflection coupling transformer in order to realize reactive damping currents of proper magnitude to readily permit power feedback into the B supply circuit of the driving vacuum tube. The use of a transformer in this connection, of course, represents certain additional costs incircuit construction as well as introducing inherent losses in the system due to leakage reactance and ma netic hysteresis. The losses incurred through use of a transformer for coupling energy from the plate circuit of the deflection driving tube to the damped deflection yoke, of course, may be obviated by direct inclusion of the yoke in the anode circuit of the vacuum tube. Generally, direct drive reaction scanning connections of this type have not been regarded as readily lending itself to high efficiency power recovery operation. However, in my co-pending U. S. patent application, Serial No. 62,844 filed December 1, 1948 entitled Power Recovery Damping System, I have described a novel power recovery damping arrangement particularly suited for television use. With such a circuit, extreme care must be exercised in its operation if proper deflection current waveforms are to be realized. As is now known in the art, the screen flatness 15 Claims. (Cl. 31527) of most present-day cathode ray image reproducing tubes makes it oftentimes desirable to purposely distort the sawtooth current waveform throughthe yoke in order to achieve an actual linear distribution of scan on the tube face.

Furthermore, in television receiver applications, the direct drive arrangement for the deflection yoke has in the past displayed another awkward feature, that being the difliculty of obtaining from the deflection system an economical form of pulse step-up power supply for development of an acelerating potential for the associated cathode ray reproducing device. In a co-pending application by Simeon I. Tourshou and William E. Scull, Jr., Serial No. 56,562 filed October 26, 1948, entitled High Voltage Power Supply, this latter difiiculty has been overcome in part through the use of an autotransformer having its primary connected in series with the deflection yoke circuit. The high voltage pulses appearing in the secondary winding are then rectified to produce the appropriate high unidirectional beam accelerating potential. The inclusion of this autotransformer primary in the yoke circuit does, however, reduce to a considerable extent the operating voltage actually supplied to the anode of the output tube and consequently a somewhat higher B+ power supply potential is normally required to correct for this voltage drop. This provision of such an increase in the initial B potential demands considerable additional cost in the design of the television receiver low voltage power supply.

The present invention aims to provide a high efiiciency low cost reaction scanning system of the direct drive B boost typewhich overcomes some of the disadvantages hereinabove set forth.

It is therefore a purpose of the present invention to provide certain improvements in my co-pending U. S. patent application, Serial No. 62,844 filed December 1, 1948, entitled Power Recovery Damping System which enables it to be more satisfactorily applied in present-day television systems.

It is another purpose of the present invention to'provide an improved form of reaction scanning power recovery damping system for direct drive electromagnetic beam deflection systems which exhibits an efficient B boost action with an attendant high degree of deflection linearity.

Another object of the present invention rests in the provision of a novel and simple B boost circuit for direct coupled electromagnetic cathode ray beam deflection yokes in which energy from an associated reaction scanning damping circuit is recovered for B boost action and in which such a B boost recovery action is compensated in the reaction scanning cycle to provide substantially linear deflection operation.

It is another purpose of the present invention to provide an improved form of deflection circuit for television systems wherein a portion 3f the cyclically damped reactive energy in the yoke circuit is applied for efiectively boosting the available polarizing potential of the driving vacuum tube.

Still another object of the present invention resides in the provision of a novel form of power recovery system particularly applicable to directly driven electromagnetic deflection coils in television systems wherein the deflection coils are included in the series with the anode-cathode circuit of the deflection system driving vacuum tube.

The present invention has numerous other objects and features of advantage, some of which, together with the foregoing will be set forth in the following description of specific apparatus embodying and utilizing the inventions novel method. It is therefore to be understood that the present invention is not limited in any way to the apparatus shown in the specific embodiments as other advantageous applications in accord with the present invention, as set forth in the appended claims, will occur to those skilled in the art after having benefited from the teachings of the following description especially when considered in connection with the accompanying drawings in which:

Figure 1 is a block-schematic representation of one form of the present invention when applied to a television sweep deflection arrangement.

Referring now to Figure 1, there is shown a portion of a typical television deflection system. Here synchronizing pulses are applied at terminal I!) to synchronize the operation of deflection signal generator [2 which, in turn, produces a conventional deflection sawtooth waveform illustrated at [4. The signal M is then applied to grid N5 of a cathode follower vacuum tube 18. The anode 20 of vacuum tube I8 accordingly is connected through a dropping resistor 22 to a source 24 of anode polarizing potential. The condenser 26 establishes the anode 23 at sub stantially A. C. ground potential. A suitable cathode follower resistor 28 is connected in the cathode to ground circuit of the vacuum tube l8 so as to provide a low impedance driving source for the grid 30 of output vacuum tube 32. Other conventional driving arrangements may, of course, be employed. A suitable negative operating bias is achieved for the grid 30 by inclusion of resistor 34 in the cathode ground circuit of vacuum tube 32. Rheostat 36, connected from a source of positive potential 38 to the top of resistor 34, allows the voltage drop across resistor 34 to be sufficiently in excess of the D. C. voltage drop across cathode follower resistor 28 to establish proper negative grid biasing of the tube 32. A cathode by-pass condenser, such as 40, may be provided to reduce signal degeneration in the cathode circuit of the output tube. Screen grid 42 is conveniently supplied with a positive polarizing potential indicated as S. G.

The anode 50 of the output vacuum tube 32 is then connected to a source of positive polarizing potential having a terminal at 52 through the series circuit comprising the primary winding 54 of autotransformer 56, the first section 58 of the deflection coil X-X, a storage capacitor 60, and the second section 62 of the deflection coil X-X. In accordance with my co-pending application Serial No. 62,844, supra, damper diodes, such 64 and 66, are respectively connected through the storage capacitor lid for damping the respective sections of the deflection coils 58 and 82.

In accordance with the present invention, the connection of the series circuit comprising the deflection yoke X--X and storage capacitor 68 to the anode 56 of the output tube 32 includes a corrective winding 61, which has developed across it a corrective voltage in accordance with anode-cathode current of the vacuum tube 32. In the arrangement shown, the auxiliary corrective winding 37 is also included in the damping circuit for one section of the deflection coil XX. In the particular illustration, the corrective winding 61 is in series with the damper diode '64 in its damping connection to the deflection coil winding section 58.

As is shown, a novel form of high voltage power recovery supply for the accelerating anode :6 of the kinescope i8 is provided through the use of the autotransformer 55. This form of high voltage power supply for use in connection with deflection systems having deflection yoke directly connected in the anode-cathode circuit of the driven vacuum tube is disclosed in the abovecited co-pending application by Simeon I. Tourshou et al., Serial No. 56,562 filed October 26, 1948. As more fully described in the Tourshou et al. specification, the output tube deflection current for the yoke winding XX passes through the primary winding 54 of the autotransformer 56 and thereby induces in the autotransformer secondary 5'! high voltage positive pulses corresponding in time to the kickback pulses 5i occurring at the plate 59 of the output tube 32. These high voltage pulses are then rectified by the diode Bi! to develop a high unidirectional potential across the storage capacitor 82. The voltage appearing thereacross is further filtered through the resistor 84 acting in combination with stray circuit capacitance and applied to accelerating terminal 76 of the cathode ray tube '58. An auxiliary winding 86 of the transformer 56 may be arranged to supply heater power for the filament B3 of the high voltage rectifier Bil.

As described in my co-pending application, Serial No. 62,844 filed. December 1, 1948, the damping diodes M and operate in accordance with. basic reaction scanning deflection system operation in relationship to the individual sections of the deflection windings 58 and 32. Accordingly, the first part of the deflection cycle, which will be here considered as resulting from the reaction scanning effect of the individual diode damping, is provided by energy stored in the respective inductances 58 and S2 at the end of the retrace phase of the deflection cycle. It is well known to those skilled in the television art that immediately following the retrace or return phase of the deflection cycle, at which time there is zero current through the vacuum tube 32, the diodes 64 and 66 will become conductive to establish a reversed current flow through the respective winding sections, the current energy of which represents the stored magnetic energy in these coil sections. For instance, in the case of the diode 84, immediately following retrace the diode 64 will become conductive to pass a damping current Id in the direction of the arrow 30.

This passage of current in the direction indicated, in eifect, adds energy to the capacitor 60 thereby making the terminal 92 thereof more positive than its corresponding terminals 94. In similar fashion, the damping current of diode 66 connected to damp the second portion 62 of the yoke winding XX is in the direction of the arrow 95, and can be seen to also add energy to the capacitor 6!; and thereby cause the terminal 92 to charge positively with respect to the terminal 54. It is clear that the damping currents through the respective diodes 64 and 66 occur simultaneously so that as far as the yoke X-X is concerned a proper overall damping arrangement has been provided, the respective damping currents through the diode in practice being substantially equal.

Investigation of the circuit arrangement shows that the capacitor 55 is in fact placed in series between the positive B supply terminal at 52 and the anode 56 of the vacuum tube 32 so that any voltage developed across capacitor 60 is additively combined with the positive B supply. Thus, damped reactive energy is stored by capacitor 60 during the reaction scanning cycle and made ready for use by the tube 32 during the ensuing'driven phase of the deflection cycle.

It will be appreciated that if the storage capacitor 50 is made sufficiently large that its terminal voltage during the conduction period of the driver tube 32 Will remain substantially constant allowing the production of a substantially linear sawtooth of current through the deflection coil X-X. As is well known to those skilled in the art, it is, however, not always desirable to produce a perfect sawtooth of current in order to achieve linear scanning distribution of the beam on the face of the kinescope. Such factors as the flatness of the cathode ray tube screen surface and the non-linear flux distribution of average deflection yoke coils make it often desirable to generate through the deflection coil itself a sawtooth of current having considerable deliberate distortion of a variety tending to compensate for these factors.

According to the operation of the present invention as hereinbefore described inconnection with Figure 1, in order to achieve proper shaping of the sawtooth current through the yoke,

there is placed in the damped circuit of one of the diodes a linearity corrective winding, such as 67, across which is developed a corrective waveform in accordance with current flow through the primary 54 of the autotransformer 56. It is seen that the corrective winding 61 is in series with both the damping circuit for the diode 64, as well as in series with the path of anode-cathode current to the deflection yoke X-X. By adjusting the turns ratio of the secondary 61 relative to the primary 54 of the transformer, it is found that a desirable waveform correction results, thereby tending to make for better linearity in the distribution of beam scanning velocity on the target of the cathode ray tube 18.

Furthermore, by properly adjusting and proportioning the winding 61, certain objectionable but inherent circuit transients, normally found in direct-drive deflection circuits, particularly of the type shown in my co-pending application, Serial No. 62,844 flled December 1, 1948, are virtually eliminated.

It will, of course, be clear to those skilled in the art that the corrective winding 6'5, although conveniently associated with the pulse step-up transformer 56 in the manner shown, may in fact be a secondary winding on a separate transformer especially designed for this purpose. With such an arrangement, the separate transformer would have its primary suitably excited by anode-cathode energy derived from the output tube 32. Moreover, if desired, another corrective winding, insulated from the winding Bl but similarly excited with a corrective voltage, may be included in the damping circuit of the second clamping diode, although in practice a single corrective winding as shown in Figure 1 has been found to be generally satisfactory.

It will furthermore be seen that if a somewhat modified damping system for the deflection yoke XX be employed which utilizes only a single damping diode in shunt with the entire deflection winding 58 plus 62, the corrective influence of a winding, such as 61, would still be of value and therefore tend to reduce circuit operating transients as well as improving the waveform characteristics of the developed deflection current. Obviously, as in all cancellation systems, the phase of the voltage developed across the corrective winding 61 will be of importance and hence the transformer leakage reactance, secondary inductance and secondary reactance, as Well as stray circuit capacitance, will all play important parts in the circuit performance. However, since it has been found in practice that certain operating environment may vary considerably from one application to another and that the general arrangement shown is not overcritical in its compensation for waveform deficiencies, the exact circuit values and magnitudes of voltages involved have not been indicated.

From the foregoing, it can be seen that the applicant has provided an improved form of direct drive deflection circuit, which combines reaction scanning and B boost power recovery with an inexpensive and novel arrangement for control of the developed deflection signal waveform.

What is claimed is:

1. Ina direct drive deflection system employing an electromagnetic beam deflection yoke, the

combination of, an output discharge tube having at least an anode and a cathode, a storage capacitor connected with the beam deflection yoke to form a series combination, connections placing the series combination in series with the anode-cathode circuit of said output tube, a signal generating device having .an output responsive to current flow through said discharge tube, a unilaterally conductive damping device, connections placing said damping device in series with the output of said signal generating device, and connections placing the series connection of said damping device and generator output in shunt with at least a portion of said deflection yoke and storage capacitor combination.

2. Apparatus according to claim 1 wherein said signal generating device comprises an electromagnetic transformer having a primary winding and a secondary winding, said primary winding being connected in series with the anode-cathode circuit of said discharge tube.

3. Apparatus according to claim 2 wherein said transformer is of the autotransformer variety.

4. In a cathode ray direct drive deflection system of the type employing an electromagnetic beam deflection yoke having an actuating winding, the combination of, a driving discharge tube having a unilaterally conductive output circuit, means responsive to current flow in said discharge tube for actively developing a control signal, connections for placing the defiectionyoke' actuating winding directly in series with theoutput circuit of said discharge tube, aunilaterally conductive damping device connected in shunt with at least a portion of said yoke actuating winding, and waveform control means for placing the developed control signal in series with the connection of said clamping device to said yoke actuating winding.

5.- Apparatus according to claim 4 wherein there is additionally provided a storage capacitor in series with said yoke in its connection in saiddischarge tube output circuit, said storage capacitor being concomitantly and further imposediin serieswith said damping device in its connection to said damping device.

6. Apparatus according to claim 5 wherein said means responsive to current flow in said dischargetube comprises an electromagnetic transformer. having its primary and secondary serially connected with said yoke actuating winding and wherein said waveform control means comprises the-inclusion of said transformer secondary winding in series with the connection of said damp ing, device to said yoke actuating winding.

7. Apparatus according to claim i wherein said means responsive to current flow in said discharge tube comprises an electromagnetic trans former having its primary and secondary serially connectedwith said yoke actuating winding and wherein-said waveform control means comprises the inclusion of said transformer secondary windingdn series with the connection of said damping device-to said yoke actuating winding.

8. In a damping circuit for an electromagnetic cathoderray beam deflection yoke directly connected in the output circuit of a driving discharge. tube, the combination of, a transformer having a primary and secondary means for connec-tingasaid transformer primary in series with said deflection yoke, a damping discharge path for said deflection yoke and connected in shunt therewith, and means for connecting "said transformer secondary: in series with the shunt connectionuof said discharge path across saiddeflection yoke.

9. Apparatus according to claim 8 wherein the driving discharge tube has at least an anode and cathode defining its-output circuit with said deflection yoke connected therebetween and where in there is-acapacitor connected in series with said deflection yoke in its-connection between said discharge tube anode and cathode.

10. In a cathode ray tube con'ibination'deflection circuit and second anode high voltage power supply circuit, the combination of, anoutput discharge tube having at least an anode and cathode, a high voltage pulse step-up transformer having a primary winding and high voltage secondary winding, an auxiliary control winding on said step-untransformer for developing a signal voltage responsive to discharge tube anode-cathode current variations, an electromagnetic deflection yoke having a deflection winding, aunilaterally conductive damping device for said deflection yoke, connections serially placing'in said anodecathode circuit the series combination of said step-up transformer primary winding and at least a portion of said deflection yoke deflection Winding, and..connections placing the seriescombinatioirofsaid damping device and said auX-- iliary control winding in shunt withat least a portion of saiddeflection yoke deflection winding.

11'. Ina cathode ray tube combination deflectionw circuit andsecond anode high'voltage power.

supply circuit, thecombinationof, an output dis-- tion yoke deflection winding, and connections placing the series combination of said damping device and said auxiliary control winding in shunt with at least a portion of said deflection yoke deflection winding.

12. In a cathode ray tube combination deflection circuit and second anode high voltage power supply circuit, the combination of, an output discharge tube having at least an anode and cathode, a high voltage pulse step-up transformer having a primary winding and high voltage secondary winding, an auxiliary control winding on said step-up transformer for developing asignal .voltage responsive to discharge tube anode-cathode current variations, anelectromagnetic deflection yoke having a deflection winding, a unilaterally conductive damping. device for saiddeflection yoke, connections. serially placing in said anodecathode circuit the series combination of said step-up transformer primary winding and at least a portion of said deflection yoke deflection winding, a storage capacitor, connections serially placing in said discharge tube anode-cathode circuit the series combination of said step-up transformor primary winding, said step-up transformer auxiliary control winding, said storage capacitorand said deflection-yoke deflectionwinding, and connections placing said damping device in shunt through said auxiliary-control winding with the series connection comprising said storage capacitor and. at least a portion of said deflection yoke deflection winding.

13. In an electromagnetic cathode ray deflection system employing a deflection coil comprising at least two separate winding sections, said coil being adapted for excitation from a vacuum tube which in turn derives its operating energy from a source of unidirectional polarizing potential, a power recovery deflection coil damping arrangement comprising in combination, a first and secondunilaterally conductive dampingdevices each separately connected for the respective dampingof one of said deflection coil winding sections during one phase of the deflection'cycle, a capacitance, means responsive to current flow through the exciting vacuurn'tuoe for developing a deflection correcting voltage, connections including said capacitor in serieswith each of said dam-ping devices and'also in series with the connection of the vacuum tube and its associated unidirectional polarizing potential, and

connections placing the developed correctingvoltage in series with atleastone of said damping devices.

14. In an electromagnetic cathode ray system employing a deflection coil comprising at least a first-and second separate windingisection, each section having aflrst and secondutilization terminals, a power recovery damping arrangement comprising in combination, a vacuum tube havingaupasso at least an anode and a cathode, said vacuum tube being connected for excitation from a source of deflection signal, a source of polarizing potential for said vacuum tube anode-cathode circuit, a capacitor connected from the first terminal of the first deflection coil winding section to the first terminal of the second deflection coil winding section, connections placing said first coil winding section second terminal and said second coil winding section second terminal in series with the anode-cathode circuit, a first unilaterally conductive damping device connected between said first coil winding section second terminal and said second coil Winding section first terminal, a second unilaterally conductive damping device connected between said first coil winding section first terminal and said coil winding section second terminal, a transformer having a primary and secondary, means connecting said transformer primary in series with the vacuum tube anode-cathode circuit, and connections placing said transformer secondary winding in series with the first unilaterally conductive damping device.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,451,641 Torsch Oct. 19, 1948 2,458,532 Schlesinger Jan. 11, 1949 2,474,666 Haantjes et a1 June 28, 1949 2,478,744 Clark Aug. 9, 1949 2,482,150 Bocciarelli Sept. 20, 1949 

